Search

Solar central receivers have inherently large time constants and time delays caused by their thermal inertia are due to the transport of the heat transfer fluid alongside the panels. This problem is even accentuated if these systems are continuously exposed to direct normal irradiance (DNI) fluctuations. Ensuring an adequate operation of this kind of process implies the adaptation of control strategies. This paper proposes a strategy that couples the temperature control of the outlet fluid while considering the heliostats' aiming points location to maintain the receiver operating below its design limit and simulates its performance under several scenarios. These tests are carried out on a non-steady-state solar plant model that considers its optical and thermal characteristics. The structure of the proposed control system is based on using intermediate flow valves along the heating flow path to reduce time delay. Hence, it renders the control system more responsive to either a DNI variation affecting the solar field or moving its operation from one state to another. The control strategy structure contains feedback and feedforward loops to determine the near-future process response to DNI measurements. It allows adding more information to the loop used to maintain the system's desired steady-state operation. The overall strategy can take the process to a steady-state operation regardless of the hour or day of operation. It produces a low variation of the outlet temperature, with a standard deviation of 3 °C, while the receiver is under a transient DNI and maintains the heliostats aimed toward the receiver without exceeding its heat flux limits. Results indicate that the proposed strategy achieves over 80% improvement based on the integral absolute error (IAE) performance index compared to conventional single-loop temperature control. Besides the simulated numerical results, this research also presents the advantages of considering intermediate mass-flow valves for control purposes of the receiver. This work should be considered a step towards improving multivariable control algorithms for the safe operation of solar central receivers. [ABSTRACT FROM AUTHOR]

The performance of solar central receivers is inherently linked to the aiming distribution/cluster of heliostats over the surface of solar receivers. A reliable methodology is necessary to maintain the lifespan of these costly devices. This research presents a method for manipulating the heliostats' aiming within a solar field by using a group behavior that relies on a single manipulated variable. This methodology addresses the problem by accounting for the heliostat position over the field, and a reduced number of the required groups. The work relies on the adaptation of an ordinary differential equation, commonly used to model conventional control valves, to establish the mean movement of the heliostats' aiming within the group. Afterward, these values are coupled to predefined paths that set the direction of motion for each point. It is shown that the proposed approach can promote changes in the heat flux profiles on the receiver, thereby allowing for the reduction of the peak heat fluxes about 30% of the initial value, while maintaining spillage below 15% for a spread aiming point distribution. Image 1 • Large groups of heliostats can work harmonized using a single primary signal. • The behavior of the group adopts the working principle of a control valve. • It enables the implementation of a vast amount of closed-loop control strategies. • New strategies allow better distribution of solar radiation over central receivers. • Reduction of heat flux peaks to 30% of the initial value with spillages below 15%. [ABSTRACT FROM AUTHOR]